diff --git a/hamster_tycoon/hamster.go b/hamster_tycoon/hamster.go
index cbe0a7c..024349a 100644
--- a/hamster_tycoon/hamster.go
+++ b/hamster_tycoon/hamster.go
@@ -32,7 +32,7 @@ type Hamster struct {
 	Name              string
 	Number            int
 	Sexe              string
-	Age               int
+	Age               int // in days
 	Father            *Hamster
 	Mother            *Hamster
 	HungerLevel       int8
@@ -44,6 +44,7 @@ type Hamster struct {
 	Gestation         bool
 	GestationPeriod   int8
 	GestationCooldown int8
+	GestationFather   *Hamster
 	Child             []*Hamster
 }
 
@@ -51,6 +52,24 @@ func (h *Hamster) Die() {
 	h.Alive = false
 }
 
+func (h *Hamster) Grow() {
+	if h.Age >= MaxAge {
+		if randNumber(h.Age-MaxAge,365) > 364 {
+			h.Die()
+			return
+		}
+	}
+	h.Age++
+	if h.Gestation {
+		h.GestationPeriod++
+	} else {
+		if h.GestationCooldown > 0 {
+			h.GestationCooldown--
+		}
+	}
+	fmt.Println(h.GestationCooldown)
+}
+
 func (h *Hamster) Fuck(another *Hamster) (bool, error) {
 	if h.Sexe == another.Sexe {
 		return false, errors.New("can't fuck together")
@@ -63,13 +82,14 @@ func (h *Hamster) Fuck(another *Hamster) (bool, error) {
 	rand := randNumber(1, 100)
 
 	if rand <= GestationLuck {
-		female := func() *Hamster {
+		female,male := func() (*Hamster,*Hamster) {
 			if h.Sexe == FEMALE {
-				return h
+				return h,another
 			} else {
-				return another
+				return another,h
 			}
 		}()
+		female.GestationFather = male
 		female.Gestation = true
 		female.GestationPeriod = 0
 		female.GestationCooldown = TotalGestationPeriod + GestationCooldown
@@ -91,7 +111,7 @@ func Born(father *Hamster, mother *Hamster) ([]*Hamster, error) {
 
 	numberOfChild := randNumberChild()
 	child := make([]*Hamster, numberOfChild)
-	for i := 1; i <= numberOfChild; i++ {
+	for i := 0; i < numberOfChild; i++ {
 		child[i] = &Hamster{
 			Name:              fmt.Sprintf("Hamster %d", GlobalHamsterNumber),
 			Number:            GlobalHamsterNumber,
diff --git a/hamster_tycoon/hamster_test.go b/hamster_tycoon/hamster_test.go
index ffcf2dc..577fd03 100644
--- a/hamster_tycoon/hamster_test.go
+++ b/hamster_tycoon/hamster_test.go
@@ -39,6 +39,104 @@ func TestHamster_Die(t *testing.T) {
 	}
 }
 
+func TestHamster_Grow(t *testing.T) {
+	testCases := []struct {
+		caseName      string
+		hamster       *Hamster
+		expectedHamster *Hamster
+	}{
+		{
+			caseName: "Age increment",
+			hamster: &Hamster{
+				Age: 0,
+				Alive: true,
+			},
+			expectedHamster: &Hamster{
+				Age: 1,
+				Alive: true,
+			},
+		},
+		{
+			caseName: "Gestation decrement",
+			hamster: &Hamster{
+				Age: 0,
+				Gestation: true,
+				GestationPeriod: 1,
+				Alive: true,
+			},
+			expectedHamster: &Hamster{
+				Age: 1,
+				Gestation: true,
+				GestationPeriod: 2,
+				Alive: true,
+			},
+		},
+		{
+			caseName: "Gestation Cooldown doesn't decrement",
+			hamster: &Hamster{
+				Age: 0,
+				Gestation: true,
+				GestationCooldown: 17,
+				GestationPeriod: 1,
+				Alive: true,
+			},
+			expectedHamster: &Hamster{
+				Age: 1,
+				GestationCooldown: 17,
+				Gestation: true,
+				GestationPeriod: 2,
+				Alive: true,
+			},
+		},
+		{
+			caseName: "Gestation Cooldown decrement",
+			hamster: &Hamster{
+				Age: 0,
+				Gestation: false,
+				GestationCooldown: 17,
+				GestationPeriod: 0,
+				Alive: true,
+			},
+			expectedHamster: &Hamster{
+				Age: 1,
+				GestationCooldown: 16,
+				Gestation: false,
+				GestationPeriod: 0,
+				Alive: true,
+			},
+		},
+		{
+			caseName: "Hamster die",
+			hamster: &Hamster{
+				Age: 365*3,
+				Gestation: false,
+				GestationCooldown: 17,
+				GestationPeriod: 0,
+				Alive: true,
+			},
+			expectedHamster: &Hamster{
+				Age: 365*3,
+				Alive:false,
+				GestationCooldown: 17,
+				Gestation: false,
+				GestationPeriod: 0,
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.caseName, func(t *testing.T) {
+			if tc.hamster.Alive == !tc.expectedHamster.Alive {
+				randomizer.FakeRandomizer(364)
+			}
+			tc.hamster.Grow()
+			if !reflect.DeepEqual(tc.hamster,tc.expectedHamster) {
+				t.Errorf("Got %v expect %v", tc.hamster, tc.expectedHamster)
+			}
+		})
+	}
+}
+
 func TestHamster_Fuck(t *testing.T) {
 	testCases := []struct {
 		caseName       string
@@ -180,31 +278,6 @@ func TestHamster_Fuck(t *testing.T) {
 	}
 }
 
-func TestBorn(t *testing.T) {
-	type args struct {
-		father *Hamster
-		mother *Hamster
-	}
-	tests := []struct {
-		name    string
-		args    args
-		want    []*Hamster
-		wantErr bool
-	}{
-		// TODO: Add test cases.
-	}
-	for _, tt := range tests {
-		got, err := Born(tt.args.father, tt.args.mother)
-		if (err != nil) != tt.wantErr {
-			t.Errorf("%q. Born() error = %v, wantErr %v", tt.name, err, tt.wantErr)
-			continue
-		}
-		if !reflect.DeepEqual(got, tt.want) {
-			t.Errorf("%q. Born() = %v, want %v", tt.name, got, tt.want)
-		}
-	}
-}
-
 func Test_randSexe(t *testing.T) {
 	tests := []struct {
 		name    string